A high power efficiency is desired for a power amplifying device used in radio communication. However, the linearity and efficiency of the power amplifying device are characteristics which are incompatible with each other. Accordingly, various distortion compensating methods have been proposed so far in order to make them compatible with each other.
FIG. 1 is a configurational diagram illustrating an example of a conventional power amplifying device. In the example illustrated in FIG. 1, a transmission signal (I, Q) is supplied to a terminal 1. The transmission signal is then supplied to a voltage control section 2 and a distortion compensating section 3. The voltage control section 2 obtains the amplitude of the transmission signal (I, Q) and generates a voltage signal which is based on this amplitude. The voltage signal is then supplied to a power source terminal of a voltage control amplifier 5 via a delay section 4.
The distortion compensating section 3 has a pre-distortion signal generating section 6 and an adaptive control section 7. The pre-distortion signal generating section 6 generates a pre-distortion signal using, for example, a series type distortion compensation system. The pre-distortion signal is then supplied to an orthogonal modulator 9 via a delay section 8 and is orthogonally modulated. The orthogonally modulated signal of a radio frequency output from the orthogonal modulator 9 is supplied to an input terminal of the voltage control amplifier 5.
The voltage control amplifier 5 performs power amplification on the orthogonally modulated signal by changing its amplification characteristic in accordance with a voltage signal supplied to the power source terminal. An output signal from the voltage control amplifier 5 is output from a terminal 11 via a directional coupler 10. Part of the orthogonally modulated signal is taken out of the directional coupler 10 and is orthogonally demodulated using an orthogonal demodulator 12. The obtained demodulated signal (I, Q) is supplied to the coefficient updating section 7 via a filter 13.
The adaptive control section 7 has a pre-distortion signal generating section 14 of the same configuration as the pre-distortion signal generating section 6, a subtractor 15, and a coefficient updating section 16.
The pre-distortion signal generating section 14 generates a pre-distortion signal from the demodulated signal and supplies the generated pre-distortion signal to the subtracter 15, and supplies the demodulated signal to the coefficient updating section 16. The subtractor 15 subtracts the pre-distortion signal which is generated from the demodulated signal and output from the pre-distortion signal generating section 14 from the pre-distortion signal which is generated from the transmission signal and output from the pre-distortion signal generating section 6 to obtain a difference between these signals and supplies the difference to the coefficient updating section 16. The coefficient updating section 6 calculates distortion compensation coefficients and supplies the calculated distortion compensation coefficients respectively to the pre-distortion signal generating sections 6 and 14 as new distortion compensation coefficients.
A technique of storing delay amount information for information on amplitude value and transmission level of an amplitude signal in the form of table data using a polar coordinates modulation system and executing delay adjustment using the information on amplitude signal and transmission level of the amplitude signal as a reference signal is proposed (see, for example, Japanese Laid-open Patent Publication No. 2006-333450).
In addition, a technique of improving the responsibility in amplitude of an output signal from an amplifier to a change in control voltage by executing amplitude adjustment on amplitude information which has been subjected to amplitude correction in a steady state using the polar coordinates modulation system is also proposed (see, for example, Japanese Laid-open Patent Publication No. 2006-197537).
In the voltage control amplifier 5 that changes the voltage signal supplied to the power source terminal in accordance with the transmission signal, timings of the voltage signal and the transmission signal supplied to the voltage control amplifier 5 are adjusted using the delay section 8. In general, the timings are adjusted upon adjustment carried out in a factory and after the timings have been adjusted in the factory, a delay amount of the delay section 8 is fixed and is not variably controlled in operation.
Therefore, such a problem is caused that in the case that a change occurs in path length characteristic between a path ranging from the voltage control section 2 to the delay section 4 and a path ranging from the distortion compensating section 3, through the delay section 8, to the orthogonal modulator 9, influenced by temperature change and aged deterioration of respective electronic components such as the voltage control section 2, the delay section 4, the distortion compensating section 3, the delay section 8 and the orthogonal modulator 9 making up the power amplifying device, a lag in timing is generated between the voltage signal and the transmission signal to decrease the transmission characteristic.